Powerheads are designed for the use underwater in defensive situations to kill large fish, especially sharks. Chances of being in a combative situation with a shark are remote. Rarely does a diver have to resort to killing a shark to deter an attack. However, when a situation does indicate an imminent attack, it is important to have a defensive weapon.
Several powerheads have been developed for carrying as defensive weapons by divers. Most of the powerheads fire a projectile into the body of a shark when the end of the powerhead is jammed sharply against the shark.
A description of the desirable powerhead is contained entitled "Sea-Way Fast-Load Shark Shooter" in the April, 1975, issue of Skin Diver magazine.
All of the available powerheads require hand carrying during swimming. The powerhead usually becomes cumbersome and difficult to carry while performing other operations. In some situations the need to have a powerhead is high, yet the need to actually employ the powerhead is low. Usually a diver elects to be encumbered by carrying the powerhead in the event that its need may become critical during particular dives. This has meant that the diver must carry the powerhead in his hand throughout the dive.